1. Field of the Invention
This invention relates generally to a tape guiding device, and more particularly is directed to a tape guiding device in which a guide element is subjected to ultrasonic oscillations for reducing frictional resistance to movement of a guided tape, for example, as in a video tape recorder (VTR).
2. Description of the Prior Art
It has been proposed by persons having an obligation to assign to the assignee of the present application, for example, as disclosed in Japanese Patent Application No. 63-18524, to provide a video tape recorder (VTR) with ultrasonically oscillated tape guide elements for the purpose of reducing the frictional resistance to movement of the tape resulting from the sliding engagement of the tape with the guide elements. For example, as shown in FIG. 1, it has been proposed to provide a VTR 1 of the open reel type with tape guiding devices 2A and 2B for guiding a magnetic recording tape T to and from, respectively, the peripheral surface of a rotary head drum 3. As shown on FIGS. 2 and 3, each of the tape guiding devices 2A and 2B includes a cylindrical guide element 4 which extends upwardly from, and is secured at its lower end to a free end portion 5a of a respective guide support member 5 so that the tape T may slidably engage and be guided by the peripheral surface of the upstanding cylindrical guide element 4. The guide support member or holder 5 is shown to be generally elongated and formed intermediate its ends, with a recess 5b opening laterally at one side of the support member and accommodating an ultrasonic oscillation generating transducer 6, which may be comprised of a stack or lamination of piezo-electric plates. The stack or lamination of piezo-electric plates is shown to be arranged generally parallel to the longitudinal axis of the guide support member 5, and the end plates of the transducer 6 engage against the adjacent ends of the recess 5b at one side of the longitudinal axis of the guide support member 5. Thus, when the stack of piezo-electric plates making up the transducer 6 expands and contracts, as indicated by the arrows 7 on FIGS. 2 and 3, the guide support member 5 is flexed laterally causing its free end portion 5a to oscillate laterally as indicated by the arrow 8 on FIG. 3, for example, between the positions shown in full lines and in broken lines at 5a and 5'a which show an exaggerated oscillation for the purposes of illustration. Of course, the lateral oscillation of the free end portion of the guide support member 5 is transmitted more or less to the upstanding guide element 4 mounted thereon, and it was anticipated that the resulting oscillation of the guide element 4 would be effective to substantially reduce the friction coefficient or so-called "pseudo-adhesion force" of the magnetic tape T in respect to the guide element 4, and thereby achieve improved stability of the movement of the tape in the VTR 1.
However, it has been found that, in the known arrangement, as described above with reference to FIGS. 1-3, and in which the ultrasonic energy is imparted to the tape guiding element 4 through the support member 5 for the latter, the oscillation energy generated by the ultrasonic piezo-electric transducer 6 is inadequately transferred to the guide element 4 so that the friction coefficient of the tape T in respect to the guide element 4 cannot be decreased sufficiently for achieving the desired stability of the tape movement. Further, the oscillation of the guide element 4 as a result of the action of the transducer 6 on the support member 5 is not a standing wave so that it is easily dispersed, particularly when the tape T engaging the peripheral surface of the guide element 4 is under substantial tension, as is the case when the tape guiding devices 2A and 2B are arranged with their guide elements 4 inclined from the vertical in leading the tape to and from the surface of the rotary head drum 3 in the case of a helical scan system. It has also been found that, in the case of the known arrangement shown on FIGS. 1-3, it is not possible to obtain oscillations of the guide element 4 at adequately high frequencies, for example, of about 150 KHz, and small amplitudes, for example, about 1 micron, as such high frequencies and small amplitudes cannot be well transmitted through the support member 5 to the guide element 4 supported thereon. Moreover, the described high frequencies and small amplitudes have been found to be desirable in that they effectively reduce the frictional resistance to movement of the tape relative to the guiding element or post while minimizing the extent to which the vibration is transmitted along the tape from the location where the latter is guided by the ultrasonically oscillated guide element or post.